The application of high intensity radiation to certain glasses, such as germanium doped silicate, gamma irradiated silicate, and europium doped glass, is known to produce a change in the index of refraction in the irradiated region. This phenomenon has application to a wide variety of optical devices. For example, interfering beams of ultraviolet light have been used to induce Bragg phase gratings in optical fibers, and such uv-induced gratings have been employed in fiber lasers, optical filters, polarization converters, mode converters and fiber sensors. Another potential application is fabrication of optical memories.
An impediment to the deployment of devices containing radiation-induced index changes is that not much is known concerning their long term reliability. It is known that the induced index changes diminish with time. But not enough is known to predict the decay at arbitrary time or temperature. Some applications, such as fiber lasers for undersea cable, require high tolerances over long periods of time. Some applications also require operation at elevated temperatures, posing the additional threat of environmental stress. Accordingly, there is a need for making such devices of assured reliability.